I'm lying in hospital, shaking with fear. There are no familiar faces, only doctors and midwives hovering above me, their mouths moving silently. The contractions keep coming, and I'm horribly confused. How can I be in labour when I would never have allowed myself to get pregnant?

Welcome to my subconscious, which regularly reminds me of my terror of childbirth. The nightmares started in my teens, when I decided I could never cope with giving birth; the pain would be intolerable. Since then, the merest glimpse of a heavily pregnant woman has filled me with searing panic – my hands shake, my heart races.

I had grown used to the idea that I would not have children. But when friend after friend started a family, seeing them with their babies led to a brief suspension of terror, and six months ago I got pregnant. At first, it didn't seem too worrying – after all, I had the best part of a year to go – but the anxiety has grown and grown.

The extreme fear of childbirth, tokophobia, was first identified in 2000 by Dr Kristina Hofberg, and is surprisingly common, affecting one in six women. Hofberg separates sufferers into two categories: primary tokophobes, who fear childbirth before pregnancy, and secondary ones, whose fear is ignited by a traumatic birth. Speaking as a primary, the fact that a secondary category exists says it all.

What separates tokophobia from the usual anxieties of mothers-to-be is the depth of fear. Some tokophobes think they will die; others imagine something unbearable happening. The most common trait is a fear of vaginal birth, with no corresponding dread of caesarean sections (although some women find both prospects equally terrifying). For many, the idea of a baby growing inside them is deeply unsettling. They often seek out stories to back up their fear of labour, and my recent internet history includes a shameful number of awful-but-compelling parenting sites.

Alison Ellerbrook took a similar path when she was pregnant with her daughter, Isobel. "I read everything I could on childbirth, but it only made my imagination run wild," she says. "By the third trimester, I was frequently tearful and shaking. I had panic attacks and terrible nightmares about labour. I would tell my husband, 'I can't do this.' At my NCT [National Childbirth Trust] class, people would say they were nervous too, but it wasn't the same. I was scared I was going to die."

Unfortunately for Alison, her labour turned out to be long and complicated. "I started to feel like my body wasn't my own," she says. "Towards the end I had 13 people at the bottom of the bed. I felt like a piece of meat – there was no dignity – and I was in complete shock."

She suffered flashbacks, and was later diagnosed with postnatal depression and post-traumatic stress disorder. It has taken her two years to recover. She would love a second child, but thinks it unlikely; she uses two forms of contraception – not unusual for a tokophobe – and will not countenance pregnancy again unless, at the very least, she is guaranteed a caesarean section.

Psychotherapist Graham Price, who has treated many patients with the condition, says there are some specific triggers. Victims of sexual abuse are more likely to suffer from it, as are women who are prone to anxiety. The fear can germinate after being told a particularly gruesome birth story at an inappropriately young age, or witnessing a graphic birth scene. The actor Helen Mirren is convinced that an educational video shown at school put her off labour for life. "I swear it traumatised me to this day," she said in an interview in 2007. "I haven't had children and now I can't look at anything to do with childbirth. It absolutely disgusts me."

Price says that "severe tokophobes will go to extreme lengths to avoid pregnancy: they eschew long-term relationships or secretly take contraception while pretending to be trying for a family." Some who are desperate for children get pregnant, but then terminate their pregnancies in utter panic. Others try to induce miscarriage by over-exercising, punching themselves in the abdomen or drinking and smoking. Tokophobes lose partners and husbands over the issue, and often feel judged by the people around them.

Camilla Smart, a 33-year-old DJ, has been considering having children with her long-term female partner, but isn't sure she could cope with being the birth mother. "I became aware of my fear during GCSE biology classes," she says, "when I was incredibly squeamish about the issue. Since then, it's got worse: I can't imagine having something growing inside me, and I don't think I could ever go through with a pregnancy. It doesn't seem natural for me, and I feel completely dissociated from pregnancy. It would feel like a ticking time bomb." The anxiety does not stop there. Smart fears that if her partner carries the child, she will spend nine months in terror on her behalf.

Close to the heart of every tokophobe is the right to have an elective caesarean. Any woman who considers this risks being slapped with the "too posh to push" label, but a study published in the British Journal of Obstetrics and Gynaecology in 2008 found that almost half of women who request a caesarean do so not because they are vain and shallow – but because they are scared.

Maureen Treadwell of the Birth Trauma Association says that a caesarean is often a good option for someone with tokophobia, but many are not guaranteed one. "They are told by doctors and midwives to wait and see how they feel, which only compounds their panic, leaving some to seek a termination," she says. "Such a lack of understanding of the issue seems incredibly cruel."

Of course, the majority of women don't have a traumatic birth, as Barbara Kott, a former president of the NCT and an antenatal teacher with 30 years experience, points out. "Mostly people are surprised at how much better labour is than they were expecting," she says. "Part of the problem is the frightening stories women are told when they are pregnant. For some reason, people tend to focus more on the negative stories – often involving pregnancy situations that are extremely rare – rather than the positive ones, which make up the majority. Another reason people can be anxious is because of the way childbirth is presented on TV. It's always a drama, with people being rushed into hospital bleeding heavily, and it's actually just not like that. Most births proceed in a completely straightforward manner, and for most women it is a very positive experience. I try and counteract the fear factor by making sure everyone understands how well women's bodies are designed to give birth."

Price has found that several of his patients, who have been on the brink of terminations, have been able to deliver naturally after spending time in psychotherapy working out what caused the phobia. One patient was a 25-year-old primary tokophobe who had told her husband she was infertile, while secretly taking contraception. When the contraception failed, she was shocked and planned a termination, without her husband's knowledge.

"A friend persuaded her to see me," says Price, "and we started to tackle her fear. She was very distressed at first, and convinced that my only purpose was to persuade her to go through with the pregnancy, but by learning to accept her fear and look at whether it was justified, it started to subside. In the end she decided to have the child, told her husband, and coped with a natural birth. I saw her afterwards and she said she was fearful, but it was manageable. In fact, last time I spoke to her she was planning on having another child. For people with less severe tokophobia, it is possible for the fear to disappear altogether."

Just re-reading this piece prompts a wave of panic, but I am, for the moment at least, generally able to think myself out of the most distressing thoughts. I'm also busily trying to manage the experience that lies ahead. I've hired a doula – a non-medical midwife – to be by my side on the big day(s), and I'm reading up on hypno-birthing techniques, which friends have recommended for keeping calm.

I still dearly want a caesarean though, and before we even started trying for a family, I asked my GP whether this would be possible. Back then, she said it should not be a problem; now she seems a lot less certain. I'm therefore preparing for a natural birth, trying to focus on the sensible words of NCT experts, and reminding myself that it doesn't have to be so awful – on the contrary. But I am secretly hoping for a breech birth: my passport to a surgical delivery.